Boil kohlrabi in broth for 20 minutes. Remove from heat. Remove kohlrabi from broth, but do not discard the broth. The broth will be needed for the sauce, so set it aside for later.

Cut off the tops of the kohlrabi and carve out the centers. Chop up the centers and set aside.

Cut bacon into small pieces. In a frying pan, start frying the bacon. Add onions and cook together until onions become transparent. Remove from heat. Add onions and bacon to a large bowl. To this, add ground beef (or ground meat of your choice), egg yolk, half of the cheese, salt, pepper, and chopped up kohlrabi pieces (centers you carved out from the whole kohlrabi). Mix together. Fill each kohlrabi with the meat filling.

Grease a casserole dish with a butter, then place stuffed kohlrabi into casserole dish. Cover kohlrabi with remaining cheese. Bake for 20-30 minutes.

To the broth (that the kohlrabi were boiled in), add butter and flour. Bring it up to a simmer, stirring constantly. Continue until mixture has thickened some. Turn off heat.

When kohlrabi are finished baking, remove from the oven. Plate the kohlrabi and pour sauce over each. Serve immediately.